1. Field of the Invention
The invention relates generally to the production of a modified phenol-aldehyde resin, and more particularly to the preparation and use of a modified phenol-aldehyde resin which utilizes an additional source of aldehyde, e.g., a phenol-formaldehyde resin, as a curing agent. The invention further relates to the use of such a cured resin as a binder in a process for the production of wood composites, e.g., plywood or fiberboard.
2. Description of Related Technology
Various processes may be used to produce wood composites depending on the desired final product which is desired. Synthetic resins, such as phenol-formaldehyde resins, are often used as binders in the manufacture of wood composites such as man-made pressed wood boards (e.g., waferboard, oriented strandboard ("OSB"), or fiberboard). Such wood composites may be formed in desired shapes and sizes depending on the intended use. Fiberboard, for example, may be made by various known processes including "dry" processes (e.g., a process comprising application of resin by a blender or by a blow line application), "wet" processes, or "wet-dry" processes. Various known phenol-formaldehyde resins may also be utilized as binders in the manufacture of other wood composites such as plywood.
Several useful processes are described (for example, for the production of plywood and fiberboard) in U.S. Pat. No. 4,961,795, the disclosure of which is incorporated herein by reference.
Various fast-curing phenol-formaldehyde resins have been utilized as binders in the manufacture of wood composites. Typical fast curing phenol-formaldehyde resins have (a) a high molar ratio of formaldehyde to phenol and (b) a high caustic content in order to accelerate the curing process. However, such fast-curing resins are undesirable due to (a) high levels of free formaldehyde emission during pressing and (b) the high caustic content which negatively impacts the resistance of the final product to moisture.
It is therefore desirable to produce a binder resin which (a) has a relatively fast cure time and/or (b) is resistant to high levels of moisture. In addition, it is desirable to produce a binder system in which undesirable amounts of formaldehyde will not be released into the atmosphere upon pressing. It is further desirable to produce a binder system which is convenient to use in a process such as the those described above.